In order to improve the hydrogen storage properties of Mg-based materials, ternary Mg24Y3-3 wt.% graphite (C)-x wt.% Ni (x = 0-20) nanocomposites were synthesized by mechanical ball-milling. Micro-area elemental analysis shows that the Ni and C are evenly distributed in the samples. Effect of Ni content on hydrogen absorption and desorption behavior at various temperatures was performed. Hydrogenation leads to the in situ formation of YH2/YH3 and Mg2Ni/Mg2NiH4, which has a significant catalytic effect on the hydrogen absorption and desorption kinetics. Composites with more than 3 wt% of Ni can almost reach their maximum hydrogen storage capacity within 1 min at 100 degrees C. When the Ni content increases from 0 to 20 wt%, the dehydrogenation activation energy (Ea) is reduced to 58 kJ/mol, while the desorption peak temperature is also lowered down to 282 degrees C. Two equilibrium plateaus are clearly observed in pressure composition isotherms (p-c-T) curves, which can be ascribed to the hydrogen absorption/desorption reactions of Mg/MgH2 and Mg2Ni/Mg2NiH4. In order to take account to the reversible hydrogen storage capacity and absorption/desorption kinetics, Mg24Y3-3 wt.% C-5 wt.% Ni composite is considered having the optimized hydrogen storage performance. (C) 2018 Elsevier Ltd. All rights reserved.